A is reported to have died intestate.
Upon his intestate death the property left behind by the deceased A shall devolve on all his legal heirs consisting his wife and children.
Therefore his wife C cannot become an absolute owner of entire property neither she can own half share in the property as a right if there were children to deceased A, including the predeceased children.
Therefore ascertain the list of legal heirs or successors in interest, which you can get it from the revenue department.
The grand daughter cannot become a legal heir to the deceased A, however if she was the child of the predeceased daughter then she can claim a share proportionately in respect of her deceased mother's share out of her deceased grandfather's property as a right.
What about the daughter in law, if she is the widow of the predeceased son, then she is also entitled to a legitimate share in the property.
The way you have raised this question clearly indicates that you did not obtain a legal opinion from a local lawyer before venturing into the purchase of this property.
You may better obtain a proper legal opinion from an experienced lawyer in the local at least now so that you can sail smoothly in future without becoming prey for the legal troubles in future.